Ny way to upgrade brew cask

I ended up asking this on stackoverflow, where I was able to come up with this.

if ! brew info cask &>/dev/null; then
  echo "Failed to install Cask (Homebrew Extension)"
  exit 1
fi

Yes, the brew cask virtualbox and Parallels Desktop 12 seem to be compatible. I tested them and they are working together.

Anyway if they become incompatible at some point, there are also other alternatives. As mentioned in the comments, other alternatives contain

• Parallels Desktop 12 for Mac Pro Edition where you can use the free vagrant-parallels

• also an experimental vagrant provider for xhyve > shave > Apple > Hypervisor.framework by this comment